LOELLINGITE

an iron arsenide mineral (FeAs2) that usually occurs with iron and copper sulfides in hydrothermal vein deposits. It typically occurs with impurities of cobalt, nickel, and arsenic, as at the Andreas-Berg, in the Erzgebirge of Germany; Andalusia, Spain; and Franklin, N.J. in the United States. Loellingite is classified in a group of iron, cobalt, and nickel arsenides that form orthorhombic crystals and are assigned to the sulfide minerals, though they contain very little sulfur. For detailed physical properties, see Table under sulfide mineral.